In the related art, there is a known confocal scanning microscope provided with a dispersed-light detection function (for example, see Patent Literature 1). Many confocal scanning microscopes provided with a dispersed-light detection function are employed in fluoroscopy, fluorescence is normally weak, and the amount of fluorescent light obtained per unit time is low. In addition, in the case of a confocal scanning microscope, because a specimen is scanned at high speed, the time for exciting individual points on the specimen is also short. Accordingly, in order to obtain a bright image, it is necessary to efficiently guide fluorescence, generated in a limited amount, to a light detection portion.
AS disclosed in Patent Literature 1, because the currently available confocal scanning microscope with a dispersed-light detection function utilizes a reflective diffraction grating as light-dispersing means, it is not possible to obtain a high diffraction efficiency in a wide range of wavelength bands. This is because a reflective diffraction grating is generally a surface relief diffraction grating that obtains diffracted light by utilizing a relief structure in the surface thereof, and the diffraction efficiency of a surface relief diffraction grating is about 70% at most.
Because the light-dispersing means is generally an optical element causing a large light loss, in a confocal scanning microscope with a dispersed-light detection function, reducing the light loss occurring at the light-dispersing means is effective for improving light utilization efficiency.
A technique designed to reduce the light loss occurring at the light-dispersing means is, for example, disclosed in Patent Literature 2. The technique disclosed in Patent Literature 2 focuses on the polarization dependency of a reflective diffraction grating serving as light-dispersing means and reduces the light loss occurring at the light-dispersing means by making incident light incident after converting it to an s-polarized beam, which exhibits higher diffraction efficiency.